Development of efficient sensing materials and techniques for detecting explosives has gained more attention now than ever due to the increasing worldwide terrorist threat. Among all the detection techniques available nowadays, fluorescence-quenching based chemical detection represents one of the most sensitive and convenient methods that have been widely employed in explosives identification.
Currently, aromatic molecules and conjugated polymers (when fabricated as films) are used in sensing explosives vapor via fluorescence quenching. However, the quenching efficiency of these materials is often limited by the short exciton diffusion due to the poor molecular organization and/or weak intermolecular electronic interactions. Creating sensor films that require different film thickness dependent on the desired results. Consequently, very thin films are needed to achieve desirable amplification of signal transduction, whereas a sufficiently thick film is usually required in order to produce a measurable fluorescence signature and to minimize the interference of photobleaching. Because of these limitations, there is a growing need to develop new sensing materials that enable long-range exciton migration, and thus produce sensing systems independent of film thickness and with more flexibility for device fabrication.
Meanwhile, there is a great need to develop new types of sensing materials or systems that provide increased sensitivity, as well as increased reliability (to minimize false positives) in explosives detection. The detection minimum that is set up by the Department of Homeland Security for an explosives detector or sensor is that it should be able to detect or identify the explosives source at a standoff position, which is 50 meters (ideally 100 meters) away from the explosives source. Additionally, detecting an underground landmine also demands improved efficiency in explosives sensing, as the vapor pressure of the explosives, particularly TNT, above an underground landmine is only around 40 ppt (part per trillion).